This invention relates to an antiskid brake control method for controlling the skidding of wheels of an automotive vehicle by repeatedly decreasing and increasing brake hydraulic pressure at the time of braking.
In general, antiskid brake control involves detecting skidding of a wheel at braking, eliminating skidding when this is detected by reducing the braking force acting upon the wheel, and then subsequently increasing the braking force, thereby stabilizing steering of the vehicle and making the braking distance as short as possible.
Conventionally, in antiskid brake control of this kind, brake hydraulic pressure is increased by the braking operation, and vehicle velocity V and wheel velocity V.sub.W gradually diminish. When the wheel velocity V.sub.W attains a value .alpha., which is decided by quantities related to wheel skidding, such as slip factor and the degree of wheel deceleration, brake hydraulic pressure starts to be reduced, as shown in FIGS. 6(a) and 6(b). When wheel deceleration gradually diminishes ewing te the decrease in brake hydraulic pressure, the wheel velocity V.sub.W falls to its lowest point A with respect to the vehicle velocity V, recovers and then rises again. When, after recovering, the wheel velocity V.sub.W attains a value .beta., which is decided by the aforementioned quantities relating to skidding, brake hydraulic pressure P is increased again and the braking force is enlarged. Consequently, the degree of recovery of the wheel velocity V.sub.W declines, and wheel velocity V.sub.W recovers to the maximum extent at point B, after which it diminishes again. Antiskid braking control is carried out by thus repeating this decrease and increase in brake hydraulic pressure as appropriate.
However, in such antiskid brake control according to the prior art, the value .beta. at which there is a changeover from the decrease in brake hydraulic pressure P to repressurization is decided merely by satisfying certain fixed conditions. Accordingly, in the conventional antiskid brake control apparatus, repressurization at .beta. is performed indiscriminately without relation to a change in the condition of the road surface, the frictional coefficient .mu. of which can take on various values (e.g., the road on which the vehicle is traveling at any moment can be a high-.mu. road, intermediate- or mecium-.mu. road or low-.mu. road, etc.). As a result, optimum antiskid brake control cannot always be carried out.